Soil-resistant coating for glass surfaces

ABSTRACT

A glass article which has a water-sheeting coating. In one embodiment, a glass sheet is provided bearing a sputtered water-sheeting coating comprising silica on an exterior surface and bearing a reflective coating on an interior surface. The interior surface of a sheet of glass can be coated with a reflective coating by sputtering, in sequence, at least one dielectric layer, at least one metal layer, and at least one dielectric layer. The exterior surface of the glass can be coated with a water-sheeting coating by sputtering silica directly onto the exterior surface of the sheet of glass. Both the reflective coating and the water-sheeting coating can optionally be applied during the same pass through the same sputter coating apparatus.

RELATED APPLICATIONS

This is a divisional application of U.S. application Ser. No.09/868,542, filed Feb. 2, 1999, which in turn is a national stageapplication based on PCT US99/02208, filed Feb. 2, 1999, which in turnclaims priority to U.S. Application No. 60/113,259, filed Dec. 21, 1998,all of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention provides a coating for glass substrates and thelike which resists accumulation of dirt and water stains. Coated glasssubstrates of the invention can be used in insulated glass units whereinthe coating of the invention is carried on an exterior surface of onepane of glass while a reflective coating is applied on the opposite sideof the same pane of glass.

BACKGROUND OF THE INVENTION

Keeping windows and other glass surfaces clean is a relativelyexpensive, time-consuming process. While cleaning any individual windowis not terribly troublesome, keeping a larger number of windows cleancan be a significant burden. For example, with modern glass officetowers, it takes significant time and expense to have window washersregularly clean the exterior surfaces of the windows.

Windows and other glass surfaces can become “dirty” or “soiled” in avariety of ways. Two of the primary manners in which windows can collectdirt involve the action of water on the glass surface. First, the wateritself can deposit or collect dirt, minerals or the like onto thesurface of the glass. Obviously, dirty water landing on the glass willleave the entrained or dissolved dirt on the glass upon drying. Even ifrelatively clean water lands on the exterior surface of a window, eachwater droplet sitting on the window will tend to collect dust and otherairborne particles as it dries. These particles and any other chemicalswhich become dissolved in the water will become more concentrated overtime, leaving a characteristic spot or drying ring on the glass surface.

The second way in which water tends to give a window or other glasssurface a soiled or less attractive appearance is tied to an attack onthe glass surface itself. As a droplet of even relatively clean watersits on a glass surface, it will begin to leach alkaline components fromthe glass. For a typical soda lime glass, the soda and lime will beleached out of the glass, increasing the pH of the droplet. As the pHincreases, the attack on the glass surface will become more aggressive.As a result, the glass which underlies a drying water droplet willbecome a little bit rougher by the time the water droplet completelydries. In addition, the alkaline components which were leached out ofthe glass will be redeposited on the glass surface as a drying ring.This dried alkaline material not only detracts from the appearance ofthe glass; it will also tend to go back into solution when the glasssurface is whetted again, rapidly increasing the pH of the next waterdroplet to coalesce on the glass surface.

In storing and shipping plate glass, the presence of water on thesurfaces between adjacent glass sheets is a chronic problem. One cantake steps to shield the glass from direct contact with water. However,if the glass is stored in a humid environment, water can condense on theglass surface from the atmosphere.

This becomes more problematic when larger stacks of glass are collected.Large stacks of glass have a fairly large thermal mass and will take along time to warm up. As a consequence, they will often be cooler thanthe ambient air when ambient temperature increases (e.g., in themorning), causing moisture in the air to condense on the surface of theglass. Due to limited air circulation, any moisture which does condensebetween the sheets of glass will take quite a while to dry. This givesthe condensed moisture a chance to leach the alkaline components out ofthe glass and adversely affect the glass surface. The rate of attack canbe slowed down somewhat by applying an acid to the surface of the glass.This is commonly done by including a mild acid, e.g., adipic acid, inthe separating agent used to keep glass sheets from sticking to andscratching one another.

A number of attempts have been made to enable a glass sheet to keep aclean appearance longer. One avenue of current investigation is a“self-cleaning” surface for glass and other ceramics. Research in thisarea is founded on the ability of certain metal oxides to absorbultraviolet light and photocatalytically break down biological materialssuch as oil, plant matter, fats and greases, etc. The most powerful ofthese photocatalytic metal oxides appears to be titanium dioxide, thoughother metal oxides which appear to have this photocatalytic effectinclude oxides of iron, silver, copper, tungsten, aluminum, zinc,strontium, palladium, gold, platinum, nickel and cobalt.

While such photocatalytic coatings may have some benefit in removingmaterials of biological origin, their direct impact on other materialsis unclear and appears to vary with exposure to ultraviolet light. As aconsequence, the above-noted problems associated with water on thesurface of such coated glasses would not be directly addressed by suchphotocatalytic coatings.

A number of attempts have been made to minimize the effect of water onglass surfaces by causing the water to bead into small droplets. Forexample, U.S. Pat. No. 5,424,130 (Nakanishi, et al., the teachings ofwhich are incorporated herein by reference) suggests coating a glasssurface with a silica-based coating which incorporates fluoroalkylgroups. The reference teaches applying a silicone alkoxide paint ontothe surface of the glass, drying the paint and then burning the driedpaint in air. Nakanishi, et al. stress the importance of substitutingpart of the non-metalic atoms, i.e., oxygen in a layer of SiO₂, with afluoroalkyl group. Up to 1.5% of the oxygen atoms should be sosubstituted. Nakanishi, et al. state that if less than 0.1% of theoxygen atoms are substituted with a fluoroalkyl group, the glass won'trepel water properly because the contact angle of water on the glasssurface will be less than 80°.

Such “water repellent” coatings do tend to cause water on the surface ofthe glass to bead up. If the coating is applied to an automobilewindshield or the like where a constant flow of high velocity air isblowing over the surface, this water beading effect can help removewater from the glass surface by allowing the droplets to blow off thesurface. However, in more quiescent applications, these droplets willtend to sit on the surface of the glass and slowly evaporate. As aconsequence, this supposed “water repellent” coating will not solve thewater-related staining problems noted above. To the contrary, by causingthe water to bead up more readily, it may actually exacerbate theproblem.

Other silica coatings have been applied to the surface of glass invarious fashions. For example, U.S. Pat. No. 5,394,269 (Takamatsu, etal.) proposes a “minutely rough” silica layer on the surface of glass toreduce reflection. This roughened surface is achieved by treating thesurface with a supersaturated silica solution in hydrosilicofluoric acidto apply a porous layer of silica on the glass sheet. By using amulti-component of sol gel solution, they claim to achieve a surfacewhich has small pits interspersed with small “islet-like land regions”which are said to range from about 50-200 nm in size. While thisroughened surface may help reduce reflection at the air/glass interface,it appears unlikely to reduce the water-related staining problemsdiscussed above. If anything, the porous nature of this coating appearsmore likely to retain water on the surface of the glass. In so doing, itseems probable that the problems associated with the long-term residenceof water on the glass surface would be increased.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a glass article which hasa water-sheeting coating and a method of applying such a coating. Inaccordance with a first embodiment of this invention, a glass articlehas at least one coated surface bearing a water-sheeting coating. Thiswater-sheeting coating comprises silica sputtered directly onto anexterior surface of the glass. The water-sheeting coating has anexterior face which is substantially non-porous, but which has anirregular surface. This water-sheeting coating desirably reduces thewetting angle of water on the coated surface of the glass article belowabout 25° and causes water applied to the coated surface of the glassarticle to sheet.

In accordance with a second embodiment of the invention, a window isprovided having at least one pane of glass having an exterior surfaceexposed to periodic contact with water. The exterior surface of thispane of glass has a water-sheeting coating comprising silica sputtereddirectly on the glass surface to a mean thickness of between about 15 Åand about 350 Å. This water-sheeting coating has an exterior face whichis substantially non-porous, but which has an irregular surface. Thewater-sheeting coating causes water applied to the coated surface of thepane of glass to sheet.

In a further embodiment of the invention, a sheet of glass has aninterior surface bearing a reflective coating thereon and an exteriorsurface bearing a water-sheeting coating thereon. The reflective coatingmay comprise a reflective metal layer and at least one dielectric layer.The water-sheeting coating again comprises silica sputtered directlyonto the exterior surface of the sheet of glass and this water-sheetingcoating has an exterior face which is substantially non-porous, butwhich has an irregular surface. This water-sheeting coating desirablyreduces the contact angle of water on the coated surface of the sheet ofglass below about 25° and causes water applied to the coated exteriorsurface of the pane to sheet.

As noted above, the present invention also contemplates a method ofrendering a glass surface resistant to soiling and staining. In oneembodiment, the method comprises first providing a sheet of glass havingan interior surface and an exterior surface. The interior and exteriorsurfaces of the glass are cleaned. Thereafter, the interior surface ofthe sheet of glass is coated with a reflective coating by sputtering, insequence, at least one first dielectric layer, at least one metal layer,and at least one second dielectric layer. The exterior surface of theglass is coated with a water-sheeting coating by sputtering silicadirectly onto the exterior surface of the sheet of glass. If so desired,the water-sheeting coating can be applied on the same sputter coatingapparatus used to create the reflective coating. With appropriatematerial selection, the water-sheeting coating and one of the dielectriclayers of the reflective coating may even be applied in the samesputtering chamber in an oxidizing atmosphere. If so desired, the paneof glass can be coated on both the interior surface and the exteriorsurface while maintaining the glass in a constant orientation whereinthe interior surface is positioned above the exterior surface.

In accordance with an alternative method of the invention, a sheet ofglass having an interior surface and an exterior surface is provided. Asputtering line is also provided, the sputtering line comprising aseries of sputtering chambers, each having a support for a sheet ofglass therein. At least one of the sputtering chambers comprises a dualdirection sputtering chamber having an upper target position above thesupport and a lower target position below the support. The interior andexterior surface of the glass are cleaned and, thereafter, the sheet ofglass is positioned on the support in the dual direction supportingchamber such that the interior surface is oriented toward the uppertarget and the exterior surface is oriented toward the lower target. Theupper target is sputtered to deposit a dielectric layer. This dielectriclayer may be deposited directly on the interior surface of the glass oron a film stack layer previously deposited on the interior surface ofthe glass. While the sheet of glass remains in the dual directionsputtering chamber, the lower target is sputtered to deposit awater-sheeting coating on the exterior surface of the glass. In onepossible preferred embodiment, both the upper target and the lowertarget are sputtered in an oxidizing atmosphere within the samesputtering chamber.

In yet another embodiment, the invention provides a method of coatingtwo sides of a single pane of glass or other substrate in a single passthrough a coating apparatus, regardless of the nature of the coatingbeing applied to either side of the glass. In this method, a sheet ofglass (or other substrate) having a clean interior surface and a cleanexterior surface is provided. A sputtering line is also provided, thisline comprising a series of sputtering chambers each having a supportfor a sheet of glass therein, at least one of the sputtering chamberscomprising a downward sputtering chamber having an upper targetpositioned above the support. A second of the sputtering chamberscomprises an upward sputtering chamber having a lower target positionedbelow the support. The sheet of glass or other substrate is positionedon the support in the downward sputtering chamber such that the interiorsurface is oriented toward the upper target. The upper target issputtered to deposit a coating directly on one of the interior surfaceof the glass or a film stack layer previously deposited on the interiorsurface of the glass. The sheet of glass is also positioned on thesupport in the upward sputtering chamber such that the exterior surfaceis oriented toward the lower target. The lower target is sputtered todeposit a coating on one of the exterior surface of the glass or a filmstack layer previously deposited on the exterior surface of the glass.The glass is coated on both the interior surface and the exteriorsurface while maintaining a constant orientation wherein the interiorsurface is positioned above the exterior surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a sheet of glass bearing acoating in accordance with the invention;

FIG. 2 is a schematic cross-sectional illustration of a multi-paneinsulated glass unit incorporating a water-sheeting coating of theintervention;

FIG. 3 is a schematic cross-sectional view of a laminated windowstructure of the type commonly used in automobile windshields bearing awater-sheeting coating of the invention;

FIG. 4 is a schematic illustration of a dual direction sputteringchamber for use in accordance with the intervention;

FIG. 5 is a schematic illustration of a multiple-zone dual directionsputtering chamber for use in accordance with another embodiment of theinvention;

FIG. 6 is an atomic force micrograph of a plain, uncoated surface of asheet of conventional float glass;

FIG. 7 is a graph showing a height profile across a short length of thesurface of the sheet of glass shown in FIG. 6;

FIG. 8 is a atomic force micrograph of a surface of a sheet of floatglass bearing a water-sheeting coating in accordance with the invention;

FIG. 9 is a three-dimensional representation of an area of the samesheet of float glass illustrated in FIG. 8; and

FIG. 10 is a graph similar to FIG. 7, but showing a height profileacross a short length of the surface of the water-sheeting coating shownin FIGS. 8 and 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 schematically illustrates a sheet of glass bearing a pair ofcoatings in accordance with one useful embodiment of the invention. Thesheet of glass 10 includes an exterior face 12 and an interior face 14.(The designation of “interior” and “exterior” face in the ensuingdiscussion is somewhat arbitrary. It is assumed, though, that in mostcircumstances the exterior face will be exposed to an ambientenvironment wherein it may come into contact with dirt, water and thelike. The interior face may also be oriented toward the same kind ofambient environment. In the embodiments illustrated in FIGS. 2 and 3,though, this “interior” face is actually protected and a second pane ofglass stands between this interior face and the ambient environment.)

The interior face 14 of the glass 10 bears a reflective coating 30. Asthose skilled in the art will readily recognize, this reflective coatingmay take any desired form depending on the desired properties. A widevariety of such films are known in the art and the precise nature of thereflective coating 30 is beyond the scope of the present invention.

If, for example, the glass article is to be used as a mirror, thecoating 30 may simply comprise a relative thick layer of a reflectivemetal. If so desired, a protective coating of a dielectric material maybe applied over the surface of the metal opposite the surfacing contactwith the glass. As is known in the art, this will help protect the metallayer from chemical and physical attack. One could also employ any of avariety of mirror coatings known in the art which comprise a layer of adielectric on either side of a reflective metal layer; many dichroicmirrors known in the art employ such a

In the embodiment of FIG. 1, the reflective coating 30 is typified as aninfrared reflective coating of the type commonly used in low emissivitysolar control films. Typically, such films will comprise a metal layersandwiched between a pair of dielectric layers. This structure may berepeated to further enhance the infra-reflective properties of the filmstack. One example of a useful infrared reflective film stack isdisclosed in U.S. Pat. No. 5,302,449 (Eby, et al.), the teachings ofwhich are incorporated herein by reference.

The illustrative film stack 30 of FIG. 1 includes a base coat 32 whichmay comprise one or more layers of dielectric materials. For example,this base coat 32 may comprise zinc oxide applied at a thickness ofabout 150-275 Å. A first metal layer 34 may be applied directly on topof this base coat 32. This metal may be, for example, silver applied ata thickness of between about 100 Å and about 150 Å. A second dielectriclayer 38 may be applied over the first metal layer 34. The thickness ofthis dielectric layer 38 will depend, at least in part, on whether asecond metal layer 40 will be included in the film stack. In a filmstack having two metal layers, as shown, this second dielectric layer 38may typically comprise a relatively thick layer of a metal oxide, suchas 700-750 Å of zinc oxide. If so desired, a relatively thin sacrificiallayer 36 may be applied between the metal layer 34 and the dielectriclayer 38. This will help protect the metal layer 34 during the sputterdeposition of the dielectric layer 38. The sacrificial layer 36 may, forexample, comprise a layer of titanium metal applied at a thickness of 25Å or less. This titanium metal will oxidize sacrificially during theapplication of a metal oxide dielectric 38, limiting any damage tounderlying silver layer 34.

In the illustrated film stack, a second metal layer 40 is applied overthe second dielectric layer 38. The second metal layer 40 will usuallybe made of the same material as is the first metal layer 34. Forexample, this second metal layer 40 may comprise about 125-175 Å ofsilver. Again, a sacrificial layer 42 of titanium or the like may beapplied over the metal layer 40 to protect the metal layer duringsubsequent deposition of the overlying dielectrics 44 and 46. A thirddielectric layer 44 is applied over the sacrificial layer 42. Thisdielectric layer 44 can also be a metal oxide, e.g., zinc oxide appliedat about 250-300 Å. If so desired, a protective overcoat 46 of anotherdielectric material can be applied over the dielectric layer 44. In onepreferred embodiment, this overcoat 46 may comprise a 50-60 Å layer ofSi₃N₄.

The water-sheeting coating 20 was applied to the inner surface 12 of theglass. It is preferred that this coating be applied directly on thesurface of the glass sheet 12. As the glass, which will typically be asoda/lime glass, is largely formed of silica and the water-sheetingcoating is also desirably formed of silica, this is believed to providea strong bond between these two layers and may enhance thewater-sheeting performance of the coating 20.

The water-sheeting coating 20 of the invention desirably comprisessilica deposited directly on the exterior surface 12 of the glass 10. Aswill be discussed below in connection with FIGS. 8-10, the exterior face22 of this coating 20 has an irregular surface. (This is schematicallyshown as a series of irregularly-spaced and -sized spikes on theexterior face 22 of the coating 31). Accordingly, attributing anyspecific thickness to this coating 20 will be inherently somewhatinaccurate. However, the coating 20 desirably has a median thickness ofbetween about 15 Å and about 350 Å, with a range of between about 15 Åand about 150 Å being preferred. The major benefit of this coating atthe least cost is believed to be evidenced at a range of about 20 Å toabout 120 Å. One preferred manner in which this coating 20 may beapplied to the exterior surface 12 of the glass 10 will be discussed inmore detail below.

FIG. 2 is a schematic illustration of a multi-pane insulated glass unitin accordance with a further embodiment of the invention. Insulatedglass units are well known in the art and may not be discussed in anysignificant detail here. Briefly, though, such an insulated glass unitwould generally comprise two panes of glass 10,100 held in aspaced-apart relationship by a spacer 110. In this embodiment, thewater-sheeting coating 20 carried by the exterior surface of the glass10 is oriented away from the second pane of glass 100 while thereflective coating 30 carried by the interior face of the glass 10 isoriented toward the second pane of glass 100. The spacer 110 is bondedon one side to the interior surface 102 of the second glass pane 100 andon the other side to the first glass pane 10. As is known in the art,the spacer may be bonded directly to the interior surface 14 of theglass 10 or the reflective coating 30 may extend out to the margins ofthe glass 10 and the spacer may be attached directly to that coating 30.

Typically, the spacer will be formed of metal or the like and will havea desiccant 112 retained therein. This desiccant will be allowed tocommunicate with the gas in the interpane space 115 to remove anymoisture which may seep between the panes of glass. An exterior seal 114may be carried around the external periphery of the spacer 110 to form areliable gas and moisture barrier.

FIG. 3 illustrates another application for a coated glass article of theinvention. In this embodiment, the glass sheet 10 is bonded to a secondsheet of glass 100 by an intermediate tear-resistant plastic film 130 toform a laminated structure. Such laminated window structures are wellknown in the field of automobile windows. Typically, this plastic layer130 will take the form of a relatively thick layer of polyvinylbutyralor the like which is heat-fused to the other two sheets of glass. If sodesired, the coating 30 may be omitted. More preferably, though, thereflective film 30 will comprise a heat-temperable infrared reflectivefilm. A variety of such films are known in the art and the precisenature of this film is beyond the scope of the present invention, butany suitable heat-temperable coating 30 may be used.

As noted above, the water-sheeting coating is desirably applied bysputtering, as is the reflective coating 30, if present. These separatecoatings can be applied using conventional sputtering equipment byapplying the two coatings in separate passes through a sputtering line.For example, before the reflective coating is applied, thewater-sheeting coating 20 of the invention can be applied to theexterior surface of the glass by positioning this surface of the glassbeneath a silicon target in an oxidizing sputtering atmosphere.Thereafter, a multiple-layer reflective coating can be applied using aseries of sputtering chambers in a conventional manner, with eachchamber being adapted to sputter one or more specific layers of thedesired film stack.

FIG. 4 schematically illustrates a dual direction sputtering chamber inaccordance with one embodiment of the present invention. Magnetronsputtering chambers are well known in the art and are commerciallyavailable from a variety of sources. While a thorough discussION of suchmagnetron sputtering chambers is beyond the scope of the presentdisclosure, one relatively useful structure for such a device isdisclosed in U.S. Pat. No. 5,645,699 (Sieck), the teachings of which areincorporated herein by reference.

Generally speaking, though, magnetron sputtering involves providing atarget formed of a metal or dielectric which is to be deposited on thesubstrate. This target is provided with a negative charge and arelatively positively charged anode is positioned adjacent the target.By introducing a relatively small amount of a desired gas into thechamber adjacent the target, a plasma of that gas can be established.Atoms in this plasma will collide with the target, knocking the targetmaterial off of the target and sputtering it onto the substrate to becoated. It is also known in the art to include a magnet behind thetarget to help shape the plasma and focus the plasma in an area adjacentthe surface of the target.

In FIG. 4, the sheet of glass 10 to be coated is positioned on aplurality of support rollers 210 which are spaced along the length ofthe sputtering chamber 200. While the precise spacing of these rollers210 can be varied, for reasons explained more fully below, it is desiredthat these rollers are spaced a little bit farther apart along at leasta interim length of the chamber 200 to increase the effective coatingarea from the lower target 260.

In the illustrated embodiment, the sheet of glass 10 is oriented totravel horizontally across these rollers, e.g., from left to right. Theinterior surface 14 of the glass is oriented upwardly while the exteriorsurface 12 of the glass is oriented downwardly to rest on the rollers210. (While this is probably the most typical configuration, it shouldbe understood that the relative orientation of the glass within thesputtering chamber 200 can be switched so long as the relative positionsof the upper targets 200 and the lower target 260 are also reversed. Asa consequence, it should be noted that designating these targets as“upper” and “lower” targets is simply for purposes of convenience andthe relative orientation of these elements within the sputtering chambercan easily be reversed if so desired.)

The sputtering chamber 200 shown in FIG. 4 includes two spaced-apartupper sputtering targets 220 a and 220 b. While these targets can beplanar targets, they are illustrated as being so-called rotary orcylindrical targets. These targets are arranged generally parallel toone another with a plurality of anodes 230 extending horizontally andgenerally parallel to these targets. As suggested in U.S. Pat. No.5,645,699, an intermediate anode 230 may also be positioned betweenthese two targets.

A gas distribution system is used to supply the sputtering gas to thechamber adjacent the targets 220 a and 220 b. While a variety of gasdistribution systems are known in the art, this distribution system maysimply comprise a pair of pipes 235 with a plurality of spaced-apartopenings or nozzles oriented generally toward the target.

The use of multiple targets positioned above a glass substrate in amagnetron sputtering chamber is fairly conventional in the field. Theunique aspect of the sputtering chamber 200 FIG. 4, though, is thepresence of the “lower” target 260. This target is the target used tosputter the water-sheeting coating 20 of the invention directly on theexterior surface 12 of the glass. As with the upper targets 220 a and220 b, the lower target 260 is provided with at least one, andpreferably two, anodes 270 in sufficient proximity to establish a stableplasma. The gas distribution pipes 235 shown adjacent the upper targets220 a and 220 b are undesirably far from the lower target 260 and theintermittent presence of the glass 10 will effectively divide thesputtering chamber 200 into two separate functional areas. Accordingly,it is preferred to have separate gas distribution pipes 275 positionedbeneath the gas adjacent the lower target 260 to ensure a consistentsupply of gas for the plasma adjacent the target. If so desired, thelower pipes 275 and the upper pipes 235 may be a part of the same gasdistribution system, i.e., both sets of pipes can be connected to asingle gas supply.

The nature of the gas supplied by the lower pipes 275 will depend atleast in part on the nature of the sputtering target 260. Inconventional magnetron sputtering, the target must serve as a cathode.Due to the dielectric nature of SiO₂, it can be exceedingly difficult toreliably sputter using a silica target. As a consequence, it ispreferred that the target comprise silicon metal rather than silica. Thematerial actually deposited on the exterior surface 12 of the glass canbe converted to silica by including oxygen in the gas supplied throughthe lower gas distribution pipes 275.

While the successive sheets of glass 10 will effectively divide thesputtering chamber, this does not preclude gas introduced in one area ofthe chamber from travelling elsewhere in the chamber. As it is preferredthat the lower target 260 comprise silicon metal sputtered in anoxidizing atmosphere, it is important that the sputtering of the uppertargets 220 a and 220 b not be adversely affected by the presence of anyexcess oxygen which may be introduced through the lower pipes 275. Thismay effectively preclude the use of this dual direction sputteringchamber 200 to deposit a water-sheeting coating 20 on one side of theglass sheet and an oxygen-sensitive metal on the other surface.

More advantageously, the dual direction sputtering chamber of FIG. 4 canbe used to deposit a dielectric layer on the interior surface 14 of theglass and the silica water-sheeting coating 20 on the exterior surface12 of the glass in a single chamber. The sputtered dielectric may be anitride or the like so long as the introduction of some metal oxide intothe nitride being deposited will not adversely affect the coating beingapplied. Ideally, though, the dielectric being applied to the interiorsurface 14 is an oxide (or at least a partial oxide) so that anycommingling of the gases introduced through the two sets of pipes 235and 275 will not adversely affect either the dielectric layer or thewater-sheeting coating. For example, one or both of the targets 220 aand 220 b may be made of titanium metal or TiO_(x) (where 1<X<2) and thegas introduced through both sets of gas distribution pipes 235 and 275may comprise an appropriately balanced mixture of argon and oxygen.

In conventional magnetron sputtering chambers, the spacing of therollers 210 used to support the glass is kept fairly small to permitsmaller glass substrates to be processed on the line without anysignificant risk of having the glass fall between the rollers. In orderto minimize the interference of the rollers in applying thewater-sheeting coating on the exterior surface 12 of the glass, though,this spacing may be increased. The maximum safe spacing will need to bedetermined on a case-by-case basis for a given range of anticipatedglass sizes. However, the larger the spacing between the rollersdisposed in the path from the lower target 260 to the exterior surface12 of the glass, the greater the percentage of the sputtered silicawhich will be deposited on the glass. Of course, the rollers in otherareas of the sputtering apparatus can be maintained at their normalspacing. It may be desirable to make a few of the rollers in the dualdirection sputtering chamber 200 easily removed so the chamber can beconverted from the illustrated configuration to a more conventionallyoperated chamber coating only one side of the glass and having rollersspaced more closely together.

Instead of changing the spacing between the rollers, the rollers couldinstead be made smaller in diameter. Conventional rollers are hollowmetal tubes. If so desired, the smaller diameter rollers can bestiffened, e.g., by filling them with a rigid foam. In order to maintainthe same transport speed of the glass along the support, thesesmaller-diameter rollers would have to be turned more rapidly, e.g., bymeans of a pair of gears having the desired gear ratio.

The rollers 210 can be of any conventional structure. It has been foundthat good results can be obtained by employing cylindrical aluminumrollers about which a rope of Kevlar™ is spirally wound, with theKevlar™ providing the surface with which the glass is in direct contact.

In some specific applications, the dual direction sputtering chamber 200of FIG. 4 may be sufficient to apply the entire desired coating to boththe interior and exterior surfaces of the glass. More often, though, thesputtering chamber 200 would be part of a sputtering line comprising aseries of sputtering chambers. Each sputtering chamber in the line couldinclude both an upper target and a lower target, but in mostconventional applications the film stack applied to the upper surface ofthe glass will be more complex (i.e. will comprise a series of distinctlayers of varying composition) and thicker than is the water-sheetingcoating of the invention. As a consequence, a majority of the sputteringchambers can comprise conventional, downward sputtering chambers havingonly an upper target, with no target positioned beneath the supports.

If the sputtering line comprises a combination of downward sputteringchambers and dual direction sputtering chambers 200, the position of thedual direction chambers along the sputtering line can be varied. If thewater-sheeting coating of the invention is applied by sputtering asilicon-containing target (e.g., one formed primarily of silicon orformed of silicon doped with aluminum) in an oxidizing atmosphere, oneshould not attempt to deposit an oxidizable metal layer (e.g., aninfrared reflective silver layer of the type conventionally used in lowemissivity film stacks) on the upper surface of the glass in the samechamber. Accordingly, at least those chambers used to sputter a metallayer may be operated as a downward sputtering chamber by omitting thelower target. It would be possible, though, to deposit a metal oxide(e.g., SiO₂, ZnO or SnO₂) on the upper surface of the glass in the samechamber.

Conventional wisdom would suggest to one skilled in the art that thewater-sheeting coating of the invention be applied in the firstsputtering chamber or, if necessary, the first several sputteringchambers to make sure that the water-sheeting coating is applied beforethe glass surface is damaged or soiled by contact with the rollerssupporting the glass within the chambers. Quite surprisingly, it hasbeen found that the opposite is true—the water-sheeting coating of theinvention is optimally applied in the last sputtering chamber. If morethan one dual direction sputtering chamber 200 is necessary to deposit asufficiently thick water-sheeting coating without unduly slowing downglass speed through the sputtering line, the water-sheeting coating isoptimally applied in the last few sputtering chambers.

If the water-sheeting coating of the invention is applied at thebeginning of the sputtering line, the majority of the exterior surfaceof the glass will exhibit the desired water-sheeting properties.However, the margins of the glass may not exhibit these improvedproperties on a consistent basis. This is believed to be due to a slightoverspray of the coating applied to the upper surface of the glass afterdeposition of the water-sheeting coating, wherein a very small amount ofthe material being applied to the upper surface will drift down to thelower surface and overlie the water-sheeting coating adjacent the edgesof the glass sheet. While this oversprayed coating is thin enough as tohave no readily discernable effect on the optical properties of theglass, this virtually invisible coating compromised the benefits of thewater-sheeting coating around the edges of the glass. By applying thesilica to the exterior surface of the glass toward the end of thesputtering line, the amount of overspray deposited on top of the silicacoating can be minimized and the beneficial water-sheeting effects ofthis coating can be preserved.

A dual direction sputtering chamber 200 such as that shown in FIG. 4 isbelieved to minimize the cost and maximize production efficiency inapplying coatings to both sides of the sheet of glass. Less desirably, awater-sheeting coating of the invention could be applied in one passwhile the reflective coating is applied to the other side of the glassin a second pass, flipping the glass between the passes to permit all ofthe targets to be positioned on the same side of the supports in thechamber(s). This is much less efficient than the process outlined above,though, and is not believed to be suitable for low-cost commercial glassproduction.

As the glass substrate moves through the chamber, there will be timeswhen the glass does not effectively shield the upper targets 200 a and200 b from the lower target 260 or vice versa. As a consequence,material from the upper targets will be deposited on the lower targetand material from the lower target can be deposited on one or both ofthe upper targets. The sputtering chamber 200 of FIG. 4 is ideal if theupper targets 220 a, 220 b and the lower target 260 have substantiallythe same composition. If the upper targets have a different compositionfrom the lower target, though, the cross-contamination of the differenttargets can lead to problems in sputtering or in maintaining consistentproduct quality.

At least in theory, this problem may be overcome by independentlycontrolling the power supplied to each of the sputtering targets toensure that each target is sputtering only when the glass is positionedto shield the upper and lower targets from one another. Currentcommercially available power supply controllers are not configured inthis fashion, however. Furthermore, the control logic for such anarrangement can be unduly difficult if the sputtering line is used tocoat glass substrates of varying sizes rather than a consistent size.

FIG. 5 illustrates one possible sputtering chamber 300 which can be usedto coat both the interior surface 14 and the exterior surface 12 of thesubstrate in a single pass without significant cross contamination ofthe sputtering targets. Elements serving an analogous function toelements shown in FIG. 4 bear like reference numbers, but indexed by100, e.g., the upper gas distribution pipes 335 of FIG. 5 arefunctionally analogous to the upper gas distribution pipes 235 of FIG.4.

The sputtering chamber 300 of FIG. 5 is effectively divided into threecoating zones 300 a, 300 b and 300 c by a pair of barriers 340. Somefraction of the gas in one coating zone may flow into another coatingzone, so it is best to use a similar atmosphere in all three zones.However, the barriers 340 serve to effectively limit the amount ofmaterial sputtered in one coating zone which lands on a target inanother coating zone.

In the embodiment of FIG. 5, each of the three coating zones 300 a-300 cis adapted to hold up to four targets, with two targets positioned abovethe substrate and two positioned below the substrate. Hence, there aresix upper target mounts 321-326 positioned above the path of the glassand six lower target mounts 361-366 positioned beneath the path of theglass. This allows maximum flexibility in using this single multi-zonesputtering chamber 300 to manufacture products having differentproperties. FIG. 5 schematically illustrates each of the upper targetmounts 321-326 vertically aligned with one of the lower target mounts361-366, respectively. It should be understood, however, that thetargets need not be vertically aligned in this fashion and may be moreadvantageously positioned in a horizontally staggered arrangement.

In the configuration shown in FIG. 5, the first coating zone 300 a hastwo upper targets (320 a and 320 b), but no lower targets on the lowertarget mounts 361 or 362. While a sputtering gas should be supplied tothe upper gas distribution pipes 335 and power should be supplied to theupper anodes 330 in the first coating zone, there is no need to deliverany gas to the lower gas distribution pipes 375 or any power to thelower anodes 370. The second coating zone 300 b has two lower targets360 c and 360 d, but neither of the upper target mounts 323 and 324carry sputtering targets. Similarly, the third coating zone 300 c hastwo lower targets 360 e and 360 f, but neither of the upper targetmounts 325 and 326 carry sputtering targets. Optimally (as discussedabove), the first coating zone 300 a is used to apply the outermostlayer of the reflective film stack carried by the interior surface 14 ofthe substrates while the last two coating zones 300 b and 300 c are usedto sputter the water-sheeting coating 20 on the exterior surface 12 ofthe substrates.

The arrangement of targets in the multiple-zone sputtering chamber 300of FIG. 5 is merely illustrative and it should be understood that thetarget arrangement can be varied to maximize production efficiency fordifferent products. For example, if a thicker water-sheeting coating isdesired at the same glass speed, a silicon-containing target can bemounted on each of the lower target mounts 361-366 while none of theupper target mounts 321-326 carry a target. If a thinner coating willsuffice (or if glass speed through the coating chamber is suitablyreduced), only the last two lower target mounts 325 and 326 can beprovided with targets while each of the first four upper target mounts321-324 carry sputtering targets. Of course, any one or more of thecoating zones 300 a-300 c can be operated much like the dual-directionsputtering chamber 200 of FIG. 4 by mounting targets in the upper andlower target mounts of the same zone.

The apparatus of FIGS. 4 and 5 and the method of depositing coatingsusing such coating systems is discussed in the present applicationprimarily in the context of applying a reflective film stack on one sideof the glass and a water-sheeting coating on the other side of theglass. It is to be understood, however, that this apparatus and methodcan be used to apply coatings to both sides of a pane of glassregardless of the nature of the coatings applied thereto. For example,the apparatus can be used to apply an anti-reflective coating on bothsides of a pane of glass, to apply infrared reflective coatings to bothsides of a transparent or translucent organic substrate, or to apply awater-sheeting coating to each side of the same substrate.

The advantage of the systems illustrated in FIGS. 4 and 5 is that asubstrate can be provided with a sputtered coating (regardless ofcomposition) on both sides in a single pass through the coatingapparatus while the glass is maintained in a constant orientation, i.e.wherein it does not need to be flipped, turned or otherwise manipulated.This enables the use of a simple set of standard transport rollers tomove the glass along the production line. In the absence of the presentinvention, one typically would have to either manually handle the glassto flip it and send it back through the coating apparatus in a separaterun, or use a complex glass handling system which must hold thesubstrate and flip it at some point during the production process. Thisenables glass having coatings on both sides to be produced particularlyeconomically without any loss in coating quality.

In the past, it was assumed that even if one were to coat the bottomside of the glass, contact with the rollers would mar that coating orand/or damage the bottom surface of the glass prior to application ofthe coating. Surprisingly, however, the present invention demonstratesthat both sides of the glass can be coated in a single pass withexcellent results.

The precise operating conditions (e.g. target composition, plasmacomposition, etc.) under which the water-sheeting coating of theinvention is applied can be varied as necessary to optimize thedeposition of a coating of the desired thickness. Given the presentteaching as a guide, one of ordinary skill in the art should be able toselect suitable operating conditions to apply a coating of the inventionwithout undue experimentation.

A layer of SiO₂ in accordance with the invention may be sputterdeposited using a silicon dioxide target in an inert atmosphere, butsilica is a poor conductor and it can be difficult to sputter suchdielectric materials in a DC sputtering apparatus. One could instead usea pure silicon target in an oxidizing atmosphere, but such targets aredifficult to sputter in a consistent, controlled fashion because siliconis a semiconductor. To improve sputtering and reduce arcing, it ispreferred that a target comprising silicon with about 5% aluminum besputtered in an oxidizing atmosphere.

Even if an aluminum-doped silicon target is employed, the atmosphere inthe sputtering chamber can be varied to achieve the optimum sputteringrate. While the sputtering atmosphere should be oxidizing, it need notbe pure oxygen. To the contrary, a mixture of oxygen and an inert gaswill enhance the sputtering rate. It is believed that a sputtering gascomprising oxygen and up to about 40% argon (preferably 0-20% argon)maintained at about 3×10⁻³ mbar will suffice. The power applied to thesputtering target should be optimized to reduce arcing yet maximizesputtering rate. A power of up to about 80 kW should yield acceptableresults.

One manufacturing arrangement which has been found to work well utilizesthree rotary sputtering targets of silicon doped with about 5% aluminum,with a power of about 42 kW being applied to each target. The atmospherein the sputtering chamber comprises 100% O₂ at a pressure of about2.5-4.5 mTorr. The glass substrate is moved past these sputteringtargets at about 225-500 inches per minute.

In manufacturing float glass, molten glass is floated on a bath ofmolten tin and the glass is referred to as having an upper side and alower, or “tin” side. Most commonly, when float glass is provided with areflective coating, the coating is applied to the upper side of theglass due to some minor surface imperfections in the tin side of theglass which can arise due to contact with support rollers in theannealing lehr. If a sheet of float glass 10 is to be provided with botha water-sheeting coating 20 and a reflective layer 30, it is preferredthat the upper surface of the sheet glass be used as the interiorsurface 14 of the glass to receive the reflective coating 30 while thetin side of the glass is used as the exterior surface to receive thewater-sheeting coating 20.

FIG. 6 is an atomic force micrograph of one square micron (μm) of thesurface of the tin side of an untreated sheet of float glass. FIG. 7 isa graph representing a profile of the same side of the sheet of glassalong about a 1 μm line on that surface. Both of these images wereobtained by atomic force microscopy using a Digital InstrumentsNanoscope III using a standard silicon tip.

FIGS. 6 and 7 illustrate a relatively smooth surface. While this surfaceis not perfectly smooth and it appears to have a slightly roughappearance in FIG. 6, it is important to note that the scale of theseimages is quite small. To place these images in perspective, two peaksin the profile of FIG. 7 are highlighted by a pair of arrows. The twodarker arrows toward the left in FIG. 7 (at about 0.25 μm along theabscissa) mark the beginning and the apex of a first peak A; the twolighter arrows toward the right in FIG. 7 (at about 0.9 μm along theabscissa) mark the apex and end of a second peak B. The first peak A isless than 0.7 nm in height while the second, taller peak B is only about1.7 nm tall.

FIGS. 8-10 are analogous representations of a sheet of float glass onthe tin side of which a water-sheeting coating of the invention has beenapplied. FIG. 8 is a micrograph much like FIG. 6, also representing 1μm² of the surface. FIG. 10 is a graph much like FIG. 7, but wherein theordinate axis represents a range of 20 nm rather than the smaller 5 nmrange of FIG. 7. FIG. 9 is a perspective view which highlights thesurface features of the water-sheeting coating. The smaller vertical barto the right of the primary image is a legend representing the grayscale associated with different heights from the base surface.

By comparing these two sets of figures, it appears that thewater-sheeting coating of the invention has a significantly moreirregular surface than does the uncoated surface shown in FIGS. 6 and 7.In FIG. 8, there appear to be a series of spaced-apart projectionsrising from the surface of the glass, but it is difficult to determinein this view the height of these projections. FIGS. 9 and 10 give abetter indication of the height and shapes of these projections. In FIG.10, the two darker arrows highlight the apex and end of one peak A whilethe two lighter arrows point to the apex and end of a second peak B. Incontrast to the rather small peaks in FIG. 7, the second, smaller peak Bin FIG. 10 is about 4.3 nm tall while the first peak A is nearly 10 nmtall. This is over five times as tall as the peaks illustrated in FIG.7.

It is also worth noting that the surface of the coating shown in FIGS.8-10 is uneven, but appears to be relatively non-porous. This is insharp contrast to the photomicrographs in Takamatsu et al.'s U.S. Pat.No. 5,394,269, which show a porous sol gel-derived coating having poreson the order of 50-200 nm penetrating the coating.

For reasons which are not currently understood, these images suggestthat sputter depositing silica on the surface of the glass yields acoating with a surface having a series of fairly sharp, distinct peaks.No meaningful statistical analysis of coated surfaces have beenperformed, so it is not known if FIGS. 6-10 are representative of theirrespective surfaces. As a matter of fact, it is acknowledged that theseimages could be atypical of the overall surfaces of the samples inquestion, so it may not be appropriate to attach too much significanceto the apparent differences in the surface structure of these twoglasses. However, this data does suggest that the surface of thewater-sheeting coating 20 of the invention is relatively non-porous anddiffers from an untreated float glass surface in that it issignificantly more uneven and irregular, having a number of discrete,spaced-apart peaks rising significantly above the rest of the surface.

The behavior of a sheet of glass coated with a water-sheeting coating ofthe invention is visibly different from that of a similar sheet of glassnot bearing the present coating. A glass surface bearing awater-sheeting coating 20 tends to sheet water more readily and isnoticeably easier to clean without any visible streaks or defects thanis a comparable sheet of glass under the same conditions.

To provide an accurate comparison of a coating of the invention to adirectly comparable sheet of glass not bearing the coating, acomparative sample was prepared. A plain, untreated pane of glass wasthoroughly cleaned and laid horizontally on a set of rollers. A small,square piece of glass was laid on the upper surface of the pane of glassto serve as a template covering part of the surface of the pane. Thepane and overlying template were passed into a magnetron sputteringchamber and a coating of about 35 Å of SiO₂ was deposited. The templatewas then removed, leaving a pane of glass with a water-sheeting coating20 of the invention over most of its surface, but having an uncoatedarea which was beneath the template during the sputtering operation. Theopposite side of the glass, i.e., the side of the glass facing away fromthe side provided with the SiO₂ coating, was coated with a lowemissivity, infrared-reflective film stack having two silver layersspaced apart from one another and from the glass using a plurality ofdielectric layers.

The partially coated surface of the glass pane was visibly inspected.When completely clean, the boundaries of the uncoated area whichunderlied the template during sputtering was essentially undetectable tothe unaided eye, indicating that the water-sheeting coating had aminimal impact on the basic optical properties of the glass. A finespray of atomized water droplets was sprayed on the surface using asimple, hand-operated spray bottle of the type conventionally used tospray household cleaning products. Once the spray was applied, theboundaries of the uncoated area were readily visible. The water on thearea bearing the coating 20 sheeted to an apparently uniform film ofwater, but the area without the coating had a less uniform appearance.

A conventional cleaning solution commercially available under thetrademark Windex® was sprayed on the surface of the glass pane and thesurface was wiped with a paper towel until the area bearing the coating20 appeared dry and no longer showed any visible streaks. When wipingceased, the uncoated area still had visible streaks of moisture. Whilethese visible streaks on the uncoated area eventually dried withoutleaving any substantial residual streaking on the glass, it is believedthat the average person would tend to continue to wipe this area untilall visible streaks disappeared, meaning that the person would expendless time and effort cleaning a glass article bearing a water-sheetingcoating 20 than a glass article without such a coating.

The change in surface properties brought about by the present inventionare readily discernable on a qualitative level, but it can be moredifficult to quantify these differences in a meaningful manner.Nonetheless, the following examples are believed to illustrate thedifference between an uncoated sheet of glass and a sheet of glassbearing a water-sheeting coating 20 of the invention. In each of thefollowing Experimental Examples 1-3, two test samples, Sample A andSample B, were provided. Sample A comprised a plain sheet of soda-limeglass and Sample B was a similar sheet of soda-lime glass bearing awater-sheeting coating 20 of the invention. The water sheeting coatingwas applied using three 95% silicon/5% aluminum rotary targets at apower level of 42 kW in an oxygen atmosphere of about 3.5 mT with theglass moving at a rate of about 500 inches per minute.

EXPERIMENTAL EXAMPLE 1

Both of the samples were subjected to a salt spray test in accordancewith ASTM B117 using a 5% salt solution for 250 hours. Briefly, thesamples were cleaned and placed in a Singleton SCCH #20 CorrosionCabinet at an angle of about 15-30° from vertical, with Sample B beingoriented such that the surface bearing the water-sheeting coating 20 wasoriented to face downwardly. A 5% salt solution (5 wt % sodium chloride,95 wt % distilled water) was atomized in the cabinet at about 35° C. for250 hours, with the salt solution being collected at a rate of about 1.8ml per 80 cm per hour in the collection cylinders in the cabinet.Thereafter, the samples were removed from the cabinet, rinsed, allowedto dry and visually inspected. Sample A had more numerous water spotsthan did Sample B and the water spots on Sample A were more visible thanthe light streaks on Sample B.

Each sample was then cleaned using paper towels and Windex®. The haze ofeach sample was then measured using a BVK-Gardner Haze-Gard Plusaccording to ASTM D-1003 and ASTM D-1044, employing an integratingsphere integrating light over the spectral range associated with theCIE-C standard. Sample A, the standard glass sheet, had a hazemeasurement of about 0.15% while the haze measurement on Sample B, thesample bearing a water-sheeting coating 20, was about 0.10%.

The contact angle of the water on the surface of the glass sheet wasthen measured using a commercially available measuring device, with thecontact angle for Sample B being measured on the surface bearing thecoating 20. The contact angle for Sample A was about 32 degrees; thecontact angle for Sample B was about 12 degrees.

EXPERIMENTAL EXAMPLE 2

Handling the samples with tongs, each sample was first dipped in abeaker of boiling tap water maintained at about 100° C. and held therefor about 5 seconds, after which it was deposited in a beaker of icewater maintained at about 0° C. and held there for about 5 seconds. Thisprocess was repeated 25 times. The samples were then placed in aSingleton Model SL23 humidity test chamber maintained at about 90%relative humidity at about 120° F. (about 49° C.) for about 500 hours.Each sample was then visually inspected. As in Experimental Example 1,it was determined that Sample A exhibited more numerous and more visiblewater spots than did Sample B.

Each sample was then cleaned and the haze and contact angle measurementswere taken in much the same manner outlined above in ExperimentalExample 1. The haze measurement for Sample A was 0.34% while that forSample B was 0.14%. Sample A exhibited a contact angle of about 20°while the contact angle for Sample B was about 12°.

EXPERIMENTAL EXAMPLE 3

Two samples of uncoated glass (Samples A1 and A2) and two samples ofcoated glass (Samples B1 and B2) were cleaned and their hazemeasurements were taken. Each of the uncoated samples had hazemeasurements of about 0.09% while the haze measurement for the glasswith a water-sheeting coating 20 was about 0.08%.

A cement mixture was prepared by mixing 4 ounces (about 11.5 g) ofportland cement to 1000 ml of water. Two samples of uncoated glass(Samples A1 and A2) and two samples of coated glass (Samples B1 and B2)were held in this solution for about ten minutes then removed. SamplesA1 and B1 were then rinsed liberally with water (but without anyrubbing) and allowed to dry; Samples A2 and B2 were allowed to air drywithout rinsing.

All four samples were hand cleaned using Windex® and paper towels. Theresidual soiling on Samples A1 and A2 from the cement test smearedduring this cleaning, making it more difficult to clean the glass. Incontrast, neither Samples B1 not Sample B2 smeared and both of thesesamples dried noticeably quicker than Sample A1 or Sample A2,respectively.

Once the samples had been thoroughly hand cleaned, haze and contactangle measurements were made. After the cement treatment, the haze forSamples A1 and B1 remained unchanged at 0.09% and 0.08%, respectively.The haze measurement for Sample B2 likewise remained unchanged at about0.08%, but the haze measurement for Sample A2 increased slightly fromabout 0.09% to about 0.10%. The contact angle for Samples A1 and A2 weremeasured prior to the cement treatment at about 26°; Samples B1 and B2had contact angles of about 11° at the same stage. After the cementtreatment, the contact angle for Sample A1 was about 32° while thecontact angle for Sample B1, the other rinsed sample, was about 10°. Thecontact angle for Sample A2 was about 33° while the contact angle forSample B2, the other air-dried sample, was about 14°.

EXPERIMENTAL EXAMPLE 4

The performance of glass bearing a water-sheeting coating 20 of theinvention was compared to plain, uncoated glass and to other glasscoatings which claim to make the surface easier to clean. Each samplestarted with a sheet of float glass and, aside from the uncoated glasssample, had a coating applied to a surface thereof; the sample IDassigned to each sample type and the coating applied thereto is setforth in the following table: Sample ID Coating applied 168 35 Å SiO₂sputtered using 100% O₂ 169 50 Å SiO₂ sputtered using 100% O₂ 170 50 ÅSiO₂ sputtered using 80/20 mixture of O₂/Ar 171 100 Å SiO₂ sputteredusing 80/20 mixture of O₂/Ar 173 Window Maid ™ coating, commerciallyavailable from _(———), applied in accordance with manufacturer'sinstructions 174 Glass Shield ™ coating, commercially available from_(———), applied in accordance with manufacturer's instructions 175 ClearShield ™ coating, commercially available from _(———), applied inaccordance with manufacturer's instructions 176 uncoated glass

A set of these samples were subjected to an accelerated weathering testand the contact angle and ease of cleaning was checked on a periodicbasis. In the weathering test, the samples were placed in a stainlesssteel enclosure maintained at a temperature of about 160° F. (about 71°C.). A 300W ultraviolet light source (sold by Osram under the trade nameUltra-Vitalux) was positioned toward the bottom of the enclosure andsamples were positioned at an angle of about 45° with respect tohorizontal with the bottom edges of the sample spaced about 10 inches(about 25 cm) from the bulb. Periodically, the samples were removed fromthe enclosure and the contact angle was measured in much the same manneras that outlined above. The contact angles were as follows: ContactAngle, by number of days in weathering test Sample ID 0 1 2 3 4 5 10 16813 20 169 11 14.3 17.7 21 27 33 170 11 17 25.5 34 171 6 26.5 26.5 32 3334 173 41 50 51.5 53 42 174 23 48 48.5 49 46 175 74 62 66 70 66 176 3535 31 35

In addition, the ease of cleaning the sample was tested by sprayingWindex® on the coated surface of the sample or, in the case of theuncoated sample, on the surface which was in contact with the tin bathduring the float manufacturing process. That surface was manually wipedwith a paper towel until the surface appeared to be clean andessentially streak-free. The ease of cleaning was determined on scale of1-5, with the ease of cleaning normal, uncoated glass prior to anyenvironmental exposure being defined as 3, a very easy to clean glasssurface being rated 1 and a sample which is substantially more difficultto clean being rated 5. (While this rating system is somewhatsubjective, it does give a rough qualitative indication of the ease withwhich the glass can be cleaned.) The results of this testing were asfollows: Contact Angle, by number of days in weathering test Sample ID 01 2 3 4 5 10 168 1 1.5 1.5 2 3 169 1 1.5 1.5 2 3 4 170 1 1 1 1.5 3 4 1711 3 3 3 3 4 173 4 4 4 5 5 4 4 174 5 5 5 5 5 5 5 175 5 5 5 5 5 5 5 176 33 3

The results indicate that a water-sheeting coating 20 of the inventionmakes the glass surface significantly easier to clean than either thestandard, uncoated glass or glass coated with any one of severalcommercially available coatings designed to make glass easier to clean.As a matter of fact, these commercially available coatings actually madethe glass seem more difficult to clean. (While these coatings may beeffective in some applications, it is believed that the “ease ofcleaning” standards employed in this Experimental Example are fairlyrepresentative of how an average home owner would perceive ease ofcleaning. For example, even if streaks of the cleaning fluid on the paneof glass might dry without leaving any permanent streaks, an averageperson is likely to keep wiping the area until the glass appears cleanto avoid any residual streaking.)

The advantageous effects of the water-sheeting coating of the inventiondid appear to drop off over time in this accelerated weathering test. Inparticular, after 5 days or so in this test, coatings of the inventionyielded results comparable to those achieved with uncoated glasssamples. Even after such degradation, the samples bearing awater-sheeting coating 20 had a lower contact angle and remained easierto clean than did the commercially available coatings evaluated in thesetests.

It is unclear what correlation there may be between time of ordinaryexposure to the elements and time in the accelerated weathering testused in this example. It is believed, however, that a coating 20 of theinvention will continue to show enhanced cleanability for an extendedperiod of time. As a matter of fact, preliminary tests indicate thatmuch of the benefit of the coating 20 may be restored with appropriatecleaning even after degradation in accelerated weathering testing,suggesting that the benefits of the coating can be restored relativelysimply even after they have diminished due to exposure to the elements.

While a preferred embodiment of the present invention has beendescribed, it should be understood that various changes, adaptations andmodifications may be made therein without departing from the spirit ofthe invention and the scope of the appended claims.

1. A sheet of glass having an interior surface bearing a reflectivecoating thereon and an exterior surface bearing a water-sheeting coatingthereon, the reflective coating comprising a reflective metal layer andat least one dielectric layer, the water-sheeting coating comprisingsilica sputtered directly onto the exterior surface of the sheet ofglass, the water-sheeting coating having an exterior face which issubstantially non-porous but which has an irregular surface, thewater-sheeting coating reducing the contact angle of water on the coatedexterior surface of the glass article below about 25° and causing waterapplied to the coated exterior surface of the pane to sheet.
 2. Theinvention of claim 1 wherein the reflective coating is an infraredreflective coating comprising, in sequence moving outwardly from theinterior surface of the sheet of glass, said at least one dielectriclayer, the reflective metal layer and a second dielectric layer, theinfrared reflective coating having a transmittance of at least about 70%in the visible spectrum.
 3. The invention of claim 1 further comprisinga spacer and a second sheet of glass having an interior surface, thespacer being disposed between the interior surfaces of the sheets ofglass and serving to maintain those interior surfaces in a spaced-apartparallel relationship and defining an interpane space therebetween. 4.The invention of claim 1 further comprising a tear-resistant plasticfilm and a second sheet of glass having an interior surface, theresilient plastic film being bonded on one side to the interior surfaceof one of the sheets of glass and on its other side to the interiorsurface of the other sheet of glass, thereby forming a laminatestructure.
 5. The sheet of glass of claim 1 wherein the water-sheetingcoating has a median thickness of between about 15 Å and about 350 Å. 6.The sheet of glass of claim 1 wherein the water-sheeting coating has amedian thickness of between about 15 Å and about 150 Å.
 7. The sheet ofglass of claim 1 wherein the water-sheeting coating has a medianthickness of between about 20 Å and about 120 Å.
 8. The sheet of glassof claim 1 wherein the water-sheeting coating has a median thicknessselected from the group consisting of 35 Å, 50 Å, and 100 Å.
 9. Thesheet of glass of claim 1 wherein the exterior face of thewater-sheeting coating has a series of irregularly spaced and sizedpeaks.
 10. The sheet of glass of claim 1 wherein said reflective metallayer comprises silver.
 11. The sheet of glass of claim 1 wherein saidreflective coating comprises two reflective metal layers.
 12. A sheet ofglass having an interior surface bearing a reflective coating thereonand an exterior surface bearing a water-sheeting coating thereon, thereflective coating comprising two metal layers comprising silver and atleast one dielectric layer, the water-sheeting coating comprising silicasputtered directly onto the exterior surface of the sheet of glass, thewater-sheeting coating having a median thickness of between about 15angstroms and about 150 angstroms, the water-sheeting coating having anexterior face which is substantially non-porous but which has anirregular surface, the water-sheeting coating reducing the contact angleof water on the coated exterior surface of the glass article below about25° and causing water applied to the coated exterior surface of the paneto sheet.
 13. The sheet of glass of claim 12 wherein a first of said twometal layers is silver applied at a thickness of between about 100angstroms and about 150 angstroms.
 14. The sheet of glass of claim 13where a second of said two metal layers comprises between about 125angstroms and about 175 angstroms of silver.
 15. A multiple-paneinsulating glass unit comprising two panes of glass held in aspaced-apart relationship by a spacer, a first of said two panes havingan exterior surface oriented away from a second of said two panes, saidexterior surface carrying a water sheeting coating, the first of saidtwo panes having an interior surface oriented toward the second of saidtwo panes, said interior surface carrying a reflective coating, thewater-sheeting coating comprising substantially non-porous silicadeposited directly on said exterior surface, the reflective coatingcomprising a metal layer sandwiched between a pair of dielectric layers.16. The insulating glass unit of claim 15 wherein the water-sheetingcoating has a median thickness of between about 15 angstroms and about350 angstroms.
 17. The insulating glass unit of claim 15 wherein thewater-sheeting coating has a median thickness of between about 15angstroms and about 150 angstroms.
 18. The insulating glass unit ofclaim 15 wherein the water-sheeting coating has a median thickness ofbetween about 15 angstroms and about 120 angstroms.
 19. The insulatingglass unit of claim 15 wherein the reflective coating comprises tworeflective metal layers.
 20. The insulating glass unit of claim 19wherein each of said two reflective metal layers comprises silver.